Allegations that Moscow hacked Democratic Party emails appear in keeping with tactics that President Vladimir Putin is widely believed to use in order to influence politics beyond Russia's borders.

Security experts say there is growing speculation that the Kremlin has been meddling in European politics by funding opposition movements in an effort to weaken NATO and other trans-Atlantic ties.

"The Kremlin's reach into European politics is hardly new, but newly worrying," said Jennifer Harris, a former U.S. State Department policy planning staff member and current senior fellow at the Council on Foreign Relations. "Putin likes to put out his financial tentacles to the political elite in other countries to strengthen his influence."

The contents of thousands of hacked Democratic National Committee emails were made public just before the party's national convention began Monday. Among the emails were indications that the DNC favored the presidential campaign of Hillary Clinton over Bernie Sanders. DNC Chairwoman Debbie Wasserman Schultz stepped down from her job after the leak.

Secretary of State John Kerry raised the issue of the hacking with Russia's top diplomat on Monday, but made no accusations about who was responsible. The FBI is probing the intrusion, however.

Asked by a reporter about allegations that Russia was a behind the hack, Russian Foreign Minister Sergey Lavrov replied, "I don't want to use four-letter words," according to The Associated Press. Russia's state-controlled news media have largely made denials or ignored the allegations altogether.